Following every twist and turn, it’s shot as a drama filmed over 18 months with unprecedented access to a major crime unit.

Nothing is left out – from taping up the scene and collecting evidence, to liaising with Nicholas’s family, who are wretched with grief, and narrowing down suspects.

Knifed: Nicholas with dad Carlos (Image: Channel 4)

Not even the victim’s devastating call to 999, which will leave a knot in your stomach.

"Oh f***ing hell. I’ve been stabbed really bad…” he says to the operator, before we hear a few short gasps and then silence.

We later learn he died from multiple stab wounds from a knife that was at least 14cm long.

He had no criminal record and no links to drugs or gangs, so the detectives are facing an apparently motive­less crime. Nicholas’s only contact with police was to report his bike stolen two years before.

The Murder Detectives (Image: Channel 4)

The teen was studying at college and had recently got engaged to his girlfriend Shannon, who heard the attack play out on a phone call to him that night. “Our future was just about to start,” she says. “We wanted to start a family.”

“I don’t know if I am going to get through this,” says his mum Angela, whose other son was murdered in Jamaica in 2013. A third son died of meningitis in 1997, aged three.

The team of officers gradually piece together the evidence, and a single black glove found at the scene could be a lead. “We’ll get him. It’s just a matter of time,” says one cop.